1. Technical Field
The present invention relates to a piezoelectric thin film element using a piezoelectric thin film, and a piezoelectric thin film device.
2. Description of Related Art
A piezoelectric material is processed into various piezoelectric elements in accordance with various purposes, and is widely utilized as an actuator for particularly adding voltage and generating deformation, and as functional electronic components such as a sensor that generates voltage from the deformation reversely. As the piezoelectric material utilized for the purpose of the actuator and the sensor, a lead-based material having excellent piezoelectric characteristics, and particularly Pb(Zrx-1Tix)O3, which is particularly called PZT (described as PZT hereinafter) based perovskite-type ferroelectric material has been widely used heretofore, and which is normally formed by sintering oxide composed of an individual element. At present, reduction in size and high performance of the piezoelectric element are strongly requested, while achieving the size reduction and high performance of each kind of electronic component.
However, regarding the piezoelectric material prepared by a sintering method-based manufacturing method, being a conventional manufacturing method, as its thickness is set to be thinner, and particularly as its thickness is set closer to a thickness of about 10 μm, the size of the piezoelectric material is closer to the size of a crystal grain constituting the material, and its influence can be hardly ignored. Therefore, there is a problem that variation of the characteristics and deterioration are remarkably generated, and in order to avoid such a problem, a forming method of the piezoelectric material, to which a thin film technique replacing the sintering method is applied, has been studied in recent years. Recently, a PZR thin film formed on a silicon substrate by a sputtering method is put to practical use as a piezoelectric thin film of an actuator for a high-speed and high-definition ink jet printer head (for example, see patent document 1).
Meanwhile, a piezoelectric sintered compact and a piezoelectric thin film composed of the aforementioned PZT contain about 60 to 70 wt % of lead, and therefore they are not preferable from an ecological viewpoint and from an aspect of pollution control. Therefore, development of the piezoelectric body not containing lead is desired in consideration of an environment. At present, various non-lead piezoelectric materials are examined, including potassium sodium niobate expressed by a general formula: (K1-xNax)NbO3 (0<x<1) [described as KNN hereinafter]. Such a KNN is a material having a perovskite structure, and shows relatively excellent piezoelectric characteristics as a non-lead material, and therefore is expected as a strong candidate for the non-lead piezoelectric material (for example see patent document 2).    (Patent Document 1)    Japanese Patent Laid Open Publication No. 10-286953    (Patent document 2)    Japanese Patent Laid Open Publication No. 2007-19302
However, the aforementioned KNN thin film is formed on a silicon substrate by a film forming method such as a sputtering method and a PLD method. However, a stable manufacturing method has not been established, and the present situation is that application to a product is difficult.
In order to solve the above-described problem, an object of the present invention is to stably provide a piezoelectric thin film element and a piezoelectric thin film device.
According to a first aspect of the present invention, there is provided a piezoelectric thin film element, including:
a piezoelectric thin film on a substrate, having an alkali niobium oxide series perovskite structure expressed by a general formula (K1-xNax)NbO3 (0<x<1);
wherein an intensity of a higher angle side skirt field is stronger than an intensity of a lower angle side skirt field of a diffraction peak, in a KNN (002) diffraction peak in an X-ray diffraction 2θ/θ pattern of the piezoelectric thin film element.
According to a second aspect of the present invention, there is provided a piezoelectric thin film device; including:
a piezoelectric thin film on a silicon substrate, having an alkali niobium oxide series perovskite structure expressed by a general formula (K1-XNax)NbO3(0<x<1) provided on a silicon substrate,
wherein in the KNN (002) diffraction peak in the X-ray diffraction 2θ/θ pattern of the piezoelectric thin film element, when the diffraction peak angle is set to (2θp), an angle showing the intensity of the lower angle side skirt field of the diffraction peak is set to (2θL1/20), and an angle showing the intensity of 1/20 of a peak intensity in the higher angle side skirt field of the diffraction peak is set to (2θR1/20) so as to satisfy R=(2θR1/20)−(2θP), L=(2θp)−(2θL1/20), the value of R/(R+L) is 0.54 or more.
In these cases, preferably a crystal structure of the (K1-xNax)NbO3 (0<X<1) is set in a phase boundary state of a pseudo-cubic crystal and an orthorhombic crystal. Further, preferably Na composition x of a piezoelectric thin film having an alkali niobate oxide series perovskite structure expressed by a general formula (K1-xNax)NbO3 (0<X<1), satisfies 0.49≦x≦0.63.
Further, preferably a lower electrode may be formed between the silicon substrate and the piezoelectric thin film, and an upper electrode may be formed on the piezoelectric thin film.
According to the third aspect of the present invention, the piezoelectric thin film device is provided, including: a piezoelectric thin film element, and a voltage applying part or a voltage detecting part.
According to the fourth aspect of the present invention, in the manufacturing method of the piezoelectric tin film element having the step of forming an alkali niobate oxide series perovskite structure expressed by the general formula (K1-xNax)NbO3 (0<x<1) on a silicon substrate by sputtering, the step of forming the piezoelectric thin film element includes the step of cooling the piezoelectric thin film to a room temperature after forming the piezoelectric thin film by sputtering, and further applying heat treatment thereto, so that when the diffraction peak angle is set to (2θp), an angle showing the intensity of the lower angle side skirt field of the diffraction peak is set to (2θL1/20), and an angle showing the intensity of 1/20 of a peak intensity in the higher angle side skirt field of the diffraction peak is set to (2θR1/20), satisfying R=(2θR1/20)−(2θP), L=(2θp)−(2θL1/20), the value of R/(R+L) is 0.54 or more.